The neural substrates of memory suppression: a FMRI exploration of directed forgetting.

Abstract

The directed forgetting paradigm is frequently used to determine the ability to voluntarily suppress information. However, little is known about brain areas associated with information to forget. The present study used functional magnetic resonance imaging to determine brain activity during the encoding and retrieval phases of an item-method directed forgetting recognition task with neutral verbal material in order to apprehend all processing stages that information to forget and to remember undergoes. We hypothesized that regions supporting few selective processes, namely recollection and familiarity memory processes, working memory, inhibitory and selection processes should be differentially activated during the processing of to-be-remembered and to-be-forgotten items. Successful encoding and retrieval of items to remember engaged the entorhinal cortex, the hippocampus, the anterior medial prefrontal cortex, the left inferior parietal cortex, the posterior cingulate cortex and the precuneus; this set of regions is well known to support deep and associative encoding and retrieval processes in episodic memory. For items to forget, encoding was associated with higher activation in the right middle frontal and posterior parietal cortex, regions known to intervene in attentional control. Items to forget but nevertheless correctly recognized at retrieval yielded activation in the dorsomedial thalamus, associated with familiarity-based memory processes and in the posterior intraparietal sulcus and the anterior cingulate cortex, involved in attentional processes.

Larger brain responses for TBR-R than TBR-F information in the left posterior hippocampus (left), left inferior parietal cortex (middle) and right precuneus (right). Functional statistical results (puncorrected<0.005) are overlaid to a canonical structural image. Activity estimates (arbitrary units) are displayed for the different conditions. TBR-R: items associated to a TBR instruction and subsequently recognised; TBR-F: items associated to a TBR instruction and subsequently forgotten; TBF-R: items associated to a TBF instruction and subsequently recognised; TBF-F: items associated to a TBF instruction and subsequently forgotten; New_CR: correct rejection of items not presented during the encoding session.

Larger brain responses for TBF-R than TBF-F information in the left thalamus (left), right posterior intraparietal sulcus (middle) and left anterior cingulate (right). Functional statistical results (puncorrected<0.001) are overlaid to a canonical structural image. Activity estimates (arbitrary units) are displayed for the different conditions. TBR-R: items associated to a TBR instruction and subsequently recognised; TBR-F: items associated to a TBR instruction and subsequently forgotten; TBF-R: items associated to a TBF instruction and subsequently recognised; TBF-F: items associated to a TBF instruction and subsequently forgotten; New_CR: correct rejection of items not presented during the encoding session.